This invention relates to glow-plug ignitors for diesel engines and the like, and more particularly to ignitors of this type wherein a coil of resistance wire is electrically heated to effect the ignition of the fuel mixture in the engine cylinder.
In the past various types of diesel glow-plug ignitors have been proposed and produced. Some involved heating coils which were enclosed in a metal sheath by which the coil wires were protected, the sheath becoming sufficiently incandescent to effect ignition of the combustible mixture. Such glow plugs, while operating satisfactorily to an extent, were not sufficiently rapid in their responses, resulting in slow or difficult starting of the engine.
Other types of glow plugs variously employed sheathed wires wherein perforations were provided in the sheathing for the purpose of improving the time response of the device while at the same time providing support and/or protection for the resistance wire. While the response time was improved to an extent, the heating was still much slower than that effected, for example, by high-tension gap-type plugs such as are used in gasoline and similar engines.
Yet other glow plugs have been proposed, wherein the resistance wires were fully exposed so that their incandescent condition could be utilized to the greatest advantage in speeding up the time response characteristic. These represented a further improvement in the time response but of course there still existed the built-in time lag resulting from the mass of wire and its support as they responded to the heating effect of the energizing current. The spacing between adjoining convolutions of the heating coil represented non-productive areas, insofar as the producing of heat of incandescence was concerned, and starts were often slow, with a cold engine.